org.apache.commons.collections4.trie
Class PatriciaTrie<E>

java.lang.Object
  extended by java.util.AbstractMap<K,V>
      extended by org.apache.commons.collections4.trie.AbstractBitwiseTrie<K,V>
          extended by org.apache.commons.collections4.trie.PatriciaTrie<E>
All Implemented Interfaces:
Serializable, Map<String,E>, SortedMap<String,E>, Get<String,E>, IterableGet<String,E>, IterableMap<String,E>, IterableSortedMap<String,E>, OrderedMap<String,E>, Put<String,E>, Trie<String,E>

public class PatriciaTrie<E>
extends AbstractBitwiseTrie<K,V>
implements Trie<String,E>

Implementation of a PATRICIA Trie (Practical Algorithm to Retrieve Information Coded in Alphanumeric).

A PATRICIA Trie is a compressed Trie. Instead of storing all data at the edges of the Trie (and having empty internal nodes), PATRICIA stores data in every node. This allows for very efficient traversal, insert, delete, predecessor, successor, prefix, range, and select(Object) operations. All operations are performed at worst in O(K) time, where K is the number of bits in the largest item in the tree. In practice, operations actually take O(A(K)) time, where A(K) is the average number of bits of all items in the tree.

Most importantly, PATRICIA requires very few comparisons to keys while doing any operation. While performing a lookup, each comparison (at most K of them, described above) will perform a single bit comparison against the given key, instead of comparing the entire key to another key.

The Trie can return operations in lexicographical order using the 'prefixMap', 'submap', or 'iterator' methods. The Trie can also scan for items that are 'bitwise' (using an XOR metric) by the 'select' method. Bitwise closeness is determined by the KeyAnalyzer returning true or false for a bit being set or not in a given key.

This PATRICIA Trie supports both variable length & fixed length keys. Some methods, such as prefixMap(Object) are suited only to variable length keys.

Since:
4.0
Version:
$Id: PatriciaTrie.java 1492866 2013-06-13 21:01:00Z tn $
See Also:
Radix Tree, PATRICIA, Crit-Bit Tree, Serialized Form

Nested Class Summary
protected static class AbstractPatriciaTrie.TrieEntry<K,V>
          A Trie is a set of AbstractPatriciaTrie.TrieEntry nodes.
 
Field Summary
protected  int modCount
          The number of times this Trie has been modified.
 
Constructor Summary
PatriciaTrie()
           
PatriciaTrie(Map<? extends String,? extends E> m)
           
 
Method Summary
 void clear()
           
 Comparator<? super K> comparator()
           
 boolean containsKey(Object k)
           
 Set<Map.Entry<K,V>> entrySet()
           
 K firstKey()
          Gets the first key currently in this map.
 V get(Object k)
           
 int hashCode()
          Gets the standard Map hashCode.
 SortedMap<K,V> headMap(K toKey)
           
 Set<K> keySet()
           
 K lastKey()
          Gets the last key currently in this map.
 OrderedMapIterator<K,V> mapIterator()
          Obtains a MapIterator over the map.
 K nextKey(K key)
          Gets the next key after the one specified.
 SortedMap<K,V> prefixMap(K key)
          Returns a view of this Trie of all elements that are prefixed by the given key.
 K previousKey(K key)
          Gets the previous key before the one specified.
 V put(K key, V value)
          Note that the return type is Object, rather than V as in the Map interface.
 V remove(Object k)
          
 Map.Entry<K,V> select(K key)
          Returns the AbstractPatriciaTrie.TrieEntry whose key is closest in a bitwise XOR metric to the given key.
 K selectKey(K key)
          Returns the key that is closest in a bitwise XOR metric to the provided key.
 V selectValue(K key)
          Returns the value whose key is closest in a bitwise XOR metric to the provided key.
 int size()
           
 SortedMap<K,V> subMap(K fromKey, K toKey)
           
 SortedMap<K,V> tailMap(K fromKey)
           
 Collection<V> values()
           
 
Methods inherited from class org.apache.commons.collections4.trie.AbstractBitwiseTrie
getKeyAnalyzer, toString
 
Methods inherited from class java.util.AbstractMap
clone, containsValue, equals, isEmpty, putAll
 
Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
 
Methods inherited from interface org.apache.commons.collections4.Trie
prefixMap
 
Methods inherited from interface java.util.SortedMap
comparator, firstKey, headMap, lastKey, subMap, tailMap
 
Methods inherited from interface org.apache.commons.collections4.OrderedMap
firstKey, lastKey, mapIterator, nextKey, previousKey
 
Methods inherited from interface org.apache.commons.collections4.Put
clear, put, putAll
 
Methods inherited from interface org.apache.commons.collections4.Get
containsKey, containsValue, entrySet, get, isEmpty, keySet, remove, size, values
 

Field Detail

modCount

protected transient int modCount
The number of times this Trie has been modified. It's used to detect concurrent modifications and fail-fast the Iterators.

Constructor Detail

PatriciaTrie

public PatriciaTrie()

PatriciaTrie

public PatriciaTrie(Map<? extends String,? extends E> m)
Method Detail

clear

public void clear()
Specified by:
clear in interface Map<K,V>
Specified by:
clear in interface Put<K,V>
Overrides:
clear in class AbstractMap<K,V>
See Also:
Map.clear()

size

public int size()
Specified by:
size in interface Map<K,V>
Specified by:
size in interface Get<K,V>
Overrides:
size in class AbstractMap<K,V>
See Also:
Map.size()

put

public V put(K key,
             V value)
Description copied from interface: Put
Note that the return type is Object, rather than V as in the Map interface. See the class Javadoc for further info.

Specified by:
put in interface Map<K,V>
Specified by:
put in interface Put<K,V>
Overrides:
put in class AbstractMap<K,V>
See Also:
Map.put(Object, Object)

get

public V get(Object k)
Specified by:
get in interface Map<K,V>
Specified by:
get in interface Get<K,V>
Overrides:
get in class AbstractMap<K,V>
See Also:
Map.get(Object)

select

public Map.Entry<K,V> select(K key)
Returns the AbstractPatriciaTrie.TrieEntry whose key is closest in a bitwise XOR metric to the given key. This is NOT lexicographic closeness. For example, given the keys:
  1. D = 1000100
  2. H = 1001000
  3. L = 1001100
If the Trie contained 'H' and 'L', a lookup of 'D' would return 'L', because the XOR distance between D & L is smaller than the XOR distance between D & H.

Parameters:
key - the key to use in the search
Returns:
the AbstractPatriciaTrie.TrieEntry whose key is closest in a bitwise XOR metric to the provided key

selectKey

public K selectKey(K key)
Returns the key that is closest in a bitwise XOR metric to the provided key. This is NOT lexicographic closeness! For example, given the keys:
  1. D = 1000100
  2. H = 1001000
  3. L = 1001100
If the Trie contained 'H' and 'L', a lookup of 'D' would return 'L', because the XOR distance between D & L is smaller than the XOR distance between D & H.

Parameters:
key - the key to use in the search
Returns:
the key that is closest in a bitwise XOR metric to the provided key

selectValue

public V selectValue(K key)
Returns the value whose key is closest in a bitwise XOR metric to the provided key. This is NOT lexicographic closeness! For example, given the keys:
  1. D = 1000100
  2. H = 1001000
  3. L = 1001100
If the Trie contained 'H' and 'L', a lookup of 'D' would return 'L', because the XOR distance between D & L is smaller than the XOR distance between D & H.

Parameters:
key - the key to use in the search
Returns:
the value whose key is closest in a bitwise XOR metric to the provided key

containsKey

public boolean containsKey(Object k)
Specified by:
containsKey in interface Map<K,V>
Specified by:
containsKey in interface Get<K,V>
Overrides:
containsKey in class AbstractMap<K,V>
See Also:
Map.containsKey(Object)

entrySet

public Set<Map.Entry<K,V>> entrySet()
Specified by:
entrySet in interface Map<K,V>
Specified by:
entrySet in interface Get<K,V>
Specified by:
entrySet in class AbstractMap<K,V>
See Also:
Map.entrySet()

keySet

public Set<K> keySet()
Specified by:
keySet in interface Map<K,V>
Specified by:
keySet in interface Get<K,V>
Overrides:
keySet in class AbstractMap<K,V>
See Also:
Map.keySet()

values

public Collection<V> values()
Specified by:
values in interface Map<K,V>
Specified by:
values in interface Get<K,V>
Overrides:
values in class AbstractMap<K,V>
See Also:
Map.values()

remove

public V remove(Object k)

Specified by:
remove in interface Map<K,V>
Specified by:
remove in interface Get<K,V>
Overrides:
remove in class AbstractMap<K,V>
Throws:
ClassCastException - if provided key is of an incompatible type
See Also:
Map.remove(Object)

hashCode

public int hashCode()
Gets the standard Map hashCode.

Specified by:
hashCode in interface Map<K,V>
Overrides:
hashCode in class AbstractMap<K,V>
Returns:
the hash code defined in the Map interface

comparator

public Comparator<? super K> comparator()
Specified by:
comparator in interface SortedMap<K,V>

firstKey

public K firstKey()
Description copied from interface: OrderedMap
Gets the first key currently in this map.

Specified by:
firstKey in interface SortedMap<K,V>
Specified by:
firstKey in interface OrderedMap<K,V>
Returns:
the first key currently in this map

lastKey

public K lastKey()
Description copied from interface: OrderedMap
Gets the last key currently in this map.

Specified by:
lastKey in interface SortedMap<K,V>
Specified by:
lastKey in interface OrderedMap<K,V>
Returns:
the last key currently in this map

nextKey

public K nextKey(K key)
Description copied from interface: OrderedMap
Gets the next key after the one specified.

Specified by:
nextKey in interface OrderedMap<K,V>
Parameters:
key - the key to search for next from
Returns:
the next key, null if no match or at end

previousKey

public K previousKey(K key)
Description copied from interface: OrderedMap
Gets the previous key before the one specified.

Specified by:
previousKey in interface OrderedMap<K,V>
Parameters:
key - the key to search for previous from
Returns:
the previous key, null if no match or at start

mapIterator

public OrderedMapIterator<K,V> mapIterator()
Description copied from interface: IterableGet
Obtains a MapIterator over the map.

A map iterator is an efficient way of iterating over maps. There is no need to access the entry set or use Map Entry objects.

 IterableMap map = new HashedMap();
 MapIterator it = map.mapIterator();
 while (it.hasNext()) {
   String key = it.next();
   Integer value = it.getValue();
   it.setValue(value + 1);
 }
 

Specified by:
mapIterator in interface IterableGet<K,V>
Specified by:
mapIterator in interface OrderedMap<K,V>
Returns:
a map iterator

prefixMap

public SortedMap<K,V> prefixMap(K key)
Description copied from interface: Trie
Returns a view of this Trie of all elements that are prefixed by the given key.

In a Trie with fixed size keys, this is essentially a Map.get(Object) operation.

For example, if the Trie contains 'Anna', 'Anael', 'Analu', 'Andreas', 'Andrea', 'Andres', and 'Anatole', then a lookup of 'And' would return 'Andreas', 'Andrea', and 'Andres'.

Specified by:
prefixMap in interface Trie<K,V>
Parameters:
key - the key used in the search
Returns:
a SortedMap view of this Trie with all elements whose key is prefixed by the search key

headMap

public SortedMap<K,V> headMap(K toKey)
Specified by:
headMap in interface SortedMap<K,V>

subMap

public SortedMap<K,V> subMap(K fromKey,
                             K toKey)
Specified by:
subMap in interface SortedMap<K,V>

tailMap

public SortedMap<K,V> tailMap(K fromKey)
Specified by:
tailMap in interface SortedMap<K,V>


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